Question 433589
we need to use pythoagoras' theorem

{{{a^2+b^2=c^2}}}
{{{a^2+1^2=(sqrt(17)^2)}}}
{{{a^2+1=17}}}
{{{a^2=17-1}}}
{{{a^2=16}}}
{{{a=sqrt(16)}}}
{{{a=4}}}